While static exec feature works perfectly on Linux it has certain limitations on FreeBSD. Because of missing prctl syscall or any substitution there's no simple way to make child process terminated automatically when parent gets killed. When a single nginx worker in multi-worker configuration is killed on FreeBSD it's still possible that a new exec child will be started even if the previously started child is still alive. If you use that on FreeBSD make sure you never kill a single nginx worker and always kill all.